[SalesForce] Where is metadata for custom list view on Task

Folders are strange things indeed, there are four types of folders, document, email, report and dashboard, they do not exist as a physical Metadata Type, hence you don't see them listed here. Most of the time they don't work like regular Metadata components with the rest of the API either. The Folder documentation also further hints at their slightly 'special' nature!

Folders are stored in the corresponding component directory of the package. These directories are named documents, email, reports, and dashboards. Folders do not have a text file representation—they are containers for files. For each folder, an accompanying metadata file named FolderName-meta.xml is created at the same directory level. The FolderName-meta.xml metadata file contains the metadata information for that folder, such as the accessType. For example, for a documents folder named sampleFolder, there’s a sampleFolder-meta.xml within the documents folder of the package.

You cannot retrieve just the folder itself with the Metadata API retrieve operation, you have to request at least one file for it to create the folder and the associated metadata XML file for the folder. In my testing just now i can see that you can effectively put anything you like as the type when using retrieve and it just ignores (unlike other operations that throw errors) invalid ones, most misleading!

Fortunately you can use the latest readMetadata operation combined with the listMetadata to retrieve them instead! Here is an example using the Apex Metadata API to do just that...

MetadataService.MetadataPort service = new MetadataService.MetadataPort();
List<MetadataService.ListMetadataQuery> queries = new List<MetadataService.ListMetadataQuery>();
service.SessionHeader = new MetadataService.SessionHeader_element();
service.SessionHeader.sessionId = UserInfo.getSessionId();

MetadataService.ListMetadataQuery queryDocumentFolder = new MetadataService.ListMetadataQuery();
queryDocumentFolder.type_x = 'DocumentFolder';
queries.add(queryDocumentFolder);       
MetadataService.FileProperties[] fileProperties = service.listMetadata(queries, 30);
List<String> folderNames = new List<String>();
for(MetadataService.FileProperties fileProperty : fileProperties)
    folderNames.add(fileProperty.fileName.replace('documents/', ''));

List<MetadataService.DocumentFolder> folder = 
    (List<MetadataService.DocumentFolder>) 
        service.readMetadata('DocumentFolder', folderNames).getRecords();

Retrieve Metadata Demo Further Info

This screenshot shows the Retrieve Demo from the Apex Metadata API retrieving a document file and the document folder, you can see it retrieves the document metadata file. Again this only works IF you also retrieve a file as well sadly.

NOTE: Take a look at this code to see how the above works, to try it out enter the name of your folder in the Folder field, select Document from the drop down, select any file in the folder and click Retrieve.

On the top level menu click 'migration' and select the 'retrieve' option. The XML you'll need will be similar to the one used to deploy. Notice I'm using api version 36.

<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
        <members>Account</members>
        <name>CustomObject</name>
    </types>
    <version>36.0</version>
</Package>

You can find more info about this here https://developer.salesforce.com/docs/atlas.en-us.field_history_retention.meta/field_history_retention/field_audit_trail.htm